Optical module

ABSTRACT

A wiring pattern of a circuit board comprises two reference voltage lines holding a signal line therebetween, whereas the reference voltage lines on both ends are electrically connected to a conductive bracket. The bracket covers and electrically shields lead pins connecting a light-receiving device unit or light-emitting device unit to the circuit board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical module utilized in anoptical transceiver and the like for linking and unlinking.

2. Related Background Art

In high-speed LANs (Local Area Networks), optical transceivers havewidely been in use as a module for converting digital electric signalsand optical signals to each other. In order to attain a higher densityin ports of hub apparatus and the like using such optical transceivers,SFF (Small Form Factor) has been known as a unified standard enabling asmaller size. While such SFF optical transceivers are characterized bytheir small size and low power consumption, SFP (Small Form FactorPluggable) optical transceivers making electric connectors attachablethereto and detachable therefrom without stopping devices have furtherbeen developed.

SUMMARY OF THE INVENTION

As LANs attain a higher speed, digital signals transmitted by such anSFF or SFP optical transceiver have been shifting to a gigabit band. Inthe SFF or SFP optical transceiver, due to its small size, its opticaltransmitter unit and optical receiver unit are located close to eachother, whereby they are likely to interfere with each other when dealingwith digital signals having such a high frequency. Also, they aresusceptible to external noise, whereby the sensitivity of such anoptical transceiver is more likely to be deteriorated by crosstalk ascompared with optical transceivers having a large size.

Therefore, it is an object of the present invention to provide anoptical module used in an optical transceiver or the like, whichsuppresses the interference between its optical transmitter unit andoptical receiver unit, and the influence of noise, thereby improvingcharacteristics.

For overcoming the above-mentioned problem, the present inventionprovides an optical module comprising, within a housing, a substratehaving an electronic circuit, and light-emitting and light-receivingdevice units each having an optical output or input end connected to theelectronic circuit; (1) wherein a connecting part of the electroniccircuit to the light-emitting device unit comprises respective signallines for normal and opposite phases arranged on both sides of alight-emitting device reference voltage line disposed at a center, andrespective reference voltage lines disposed on outer sides of the signallines, the signal lines and reference voltage lines being electricallyconnected to respective lead pins extending from the light-emittingdevice unit, and a conductive light-emitting device bracket whichsurrounds the lead pins extending from the light-emitting device unitand is electrically connected to the reference voltage lines on bothends of the electronic circuit; or (2) wherein a connecting part of theelectronic circuit to the light-receiving device unit comprisesrespective reference voltage lines arranged on both sides of a signalline, the signal line and reference voltage lines being electricallyconnected to respective lead pins extending from the light-receivingdevice unit, and a conductive light-receiving device bracket whichsurrounds the lead pins extending from the light-receiving device unitand is electrically connected to the reference voltage lines on bothends of the electronic circuit.

When the lead pins extending from the light-emitting device unit and/orlight-receiving device unit are electrically shielded with alight-emitting device bracket and/or light-receiving device bracket assuch while signal lines are held between reference voltage lines,potentials are stabilized, and mutual interference and influences ofexternal noise can be suppressed. As a consequence, characteristicsimprove.

Preferably, the light-emitting device bracket or light-receiving devicebracket is electrically connected to a metal part of an enclosure of itscorresponding light-emitting device unit or light-receiving device unit.This can stabilize reference voltages of the light-emitting device andlight-receiving device, whereby stable characteristics can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view showing components of an optical module(optical transceiver) in accordance with the present invention;

FIG. 2A is a view showing the light-emitting device unit of theapparatus of FIG. 1, whereas FIG. 2B is a view showing thelight-receiving device unit thereof;

FIGS. 3A and 3B are perspective views showing the light-emitting devicebracket in the apparatus of FIG. 1 at respective angles different fromeach other;

FIGS. 4A and 4B are perspective views showing the light-receiving devicebracket in the apparatus of FIG. 1 at respective angles different fromeach other;

FIG. 5 is a perspective view showing the bracket holder in the apparatusof FIG. 1, whereas FIG. 6 is a sectional view taken along the line VI—VIof FIG. 5;

FIG. 7 is a partial perspective view showing the relationship betweenthe light-emitting/receiving device unit, each bracket, and the circuitboard in the apparatus of FIG. 1;

FIG. 8 is a sectional view of the apparatus of FIG. 1 taken along theline VIII—VIII of FIG. 7;

FIGS. 9, 10, and 11A are views for explaining the state where thelight-emitting device, light-receiving device, circuit board, and thelike are attached to the housing in the apparatus of FIG. 1, the statewhere the bracket is attached thereto, and the state where the bracketholder is attached thereto, respectively, whereas FIG. 11B is anenlarged view of a part of FIG. 11A;

FIG. 12 is a graph showing EMI test results comparing the apparatus ofFIG. 1 with a conventional apparatus, whereas FIGS. 13 and 14 are graphsshowing RES test results comparing these apparatus;

FIG. 15A is a chart showing a waveform transmitted by the apparatus ofFIG. 1, whereas FIG. 15B is a chart showing a waveform transmitted by aconventional apparatus; and

FIG. 16 is a graph showing changes in characteristics vs. the number ofconnector attaching/detaching operations in the apparatus of FIG. 1,whereas FIG. 17 is a chart summarizing changes in the received waveform,transmitted waveform, and connector surface vs. the number of connectorattaching/detaching operations in the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the present invention will beexplained in detail with reference to the accompanying drawings. Formaking it easier to understand the explanation, constituents identicalto each other among the drawings will be referred to with numeralsidentical to each other whenever possible, without repeating theiroverlapping descriptions.

FIG. 1 is a view showing an optical transceiver, which is an opticalmodule in accordance with the present invention, in an exploded statesuch that its components can be understood easily. This opticaltransceiver is an SFP type optical transceiver having an elongated formwith a substantially rectangular cross section, whose one end has anoptical connector for connecting with respective optical fibers fortransmission and reception, whereas the other end has an electricconnector for inputting an electric power from the outside andtransmitting/receiving an electric signal.

The optical transceiver contains, within a housing 1, a circuit board 2mounted with an electronic circuit, and a light-receiving device unit 4and a light-emitting device unit 5 which are connected to the circuitboard 2. The light-receiving device unit 4 and light-emitting deviceunit 5 have their lead pin parts covered with respective metal brackets6, 7 having an electric shielding function, and are secured to thehousing 1 with a bracket holder 8 made of a resin. The circuit board 2is secured to the housing 1 with a stopper 3, whereas the housing 1 isshrouded with the cover 9. The actuator 10 is disposed in the housing 1near a side end part of the optical connector.

Configurations of the light-emitting device unit 5 and light-receivingdevice unit 4 will now be explained with reference to FIGS. 2A and 2B,respectively. In the light-receiving device unit 4, as shown in FIG. 2B,a metal enclosure 42 containing therewithin a light-receiving device(e.g., photodiode), an optical system, a preamplifier, and the likewhich are not depicted, and a resin ferrule 41 into which an opticalfiber is inserted from the leading end thereof are integrated with eachother. Five lead pins 43 each having a wavy leading end extend from themetal enclosure 42, among which lead pins 43 a and 43 b output a normalphase signal and an opposite phase signal which constitute complementarysignals of an electric signal corresponding to a received opticalsignal, respectively. In the remaining three lead pins, a power voltage(V_(ee)) is supplied to lead pins 43 c and 43 e, whereas lead pin 43 dis grounded (GND).

In the light-emitting device unit 5, as shown in FIG. 2A, a metalenclosure 52 containing therewithin a light-emitting device (e.g. laserdiode), an optical system, and the like which are not depicted, and aresin ferrule 51 into which an optical fiber is inserted from theleading end thereof are integrated with each other. Three lead pins 53each having a wavy leading end extend from the metal enclosure 52, amongwhich an electric signal corresponding to the optical signal to beoutputted is fed into lead pin 53 c. The power V_(cc) of the circuitboard is supplied to lead pin 53 a, whereas lead pin 53 b acts as anoutput terminal. The voltage V_(cc) may be made different from thevoltage V_(ee) supplied to the light-receiving device as well.

Structures of the brackets 6, 7 and bracket holder 8 will now beexplained. As shown in FIGS. 3A and 3B, the light-receiving devicebracket 6 has a form in which two legs 61, 62 project from asubstantially semicylindrical body 60. The body 60 has a hole 64substantially located at the center thereof, whereas a lug 63 is formedon the leg 61, 62 side of the hole 64 so as to be bent toward the insideof the body 60.

On the other hand, as shown in FIGS. 4A and 4B, the light-emittingdevice bracket 4 has a form in which two legs 71, 72 project from asubstantially semicylindrical body 70. The body 70 has a lug 73 benttoward the inside of the body 70 on the leg 71, 72 side thereof, and ahole 74 substantially located at the center thereof. The light-emittingdevice bracket 7 is a bit smaller than the light-receiving devicebracket 6, whereas the hole 74 of the former is formed smaller than thehole 64 of the latter.

As shown in FIG. 5, the bracket holder 8 has two recesses 80, 81arranged in parallel at one end, whereas semicylindrical projections 80a, 81 a are disposed on respective extensions of the recesses 80, 81.Upwardly projecting protrusions 80 a, 81 a are formed between therecesses 80, 81. Respective leading ends of the protrusions 82, 83 haveoutwardly projecting claws 82 a, 83 a (see FIG. 6). A U-shaped space 85is formed between the claws 82 a, 83 a. A side wall 84 of the bracketholder 8 at a side end of the recesses 80, 81 is a slope forming anangle of 40° to 80° with respect to the horizontal plane (bottom face ofthe recesses 82, 83). This angle is assumed to be 45° in the followingexplanation of this embodiment.

FIG. 7 is a view for explaining the state where the light-receivingdevice unit 4, light-emitting device unit 5, and brackets 6, 7 areattached to the circuit board 2, whereas FIG. 8 is a sectional view ofFIG. 1 taken along the line VIII—VIII of FIG. 7. FIGS. 9 and 10 areperspective views showing the states where the bracket is removed andattached, respectively. As shown in FIGS. 7 to 10, an end part of thecircuit board 2 opposite from the electric connector part 21 is formedwith respective wiring patterns for electrically connecting with thelight-receiving device unit 4 and light-emitting device unit 5 on eachsurface thereof. The wiring pattern to be connected to thelight-receiving device unit 4 comprises five patterns arranged inparallel so as to be orthogonal to one side of the connecting end part,among which three patterns at the center and both ends are referencevoltage supply patterns P_(VG), whereas a normal phase signal outputpattern P_(a) and an opposite phase signal output pattern P_(b) areformed at two locations, respectively, held among the patterns P_(VG).On the other hand, the wiring pattern to be connected to thelight-emitting device unit 5 comprises three patterns arranged inparallel so as to be orthogonal to one side of the connecting end part,among which the center one is a pattern P_(pd) for supplying a signalcorresponding to an optical signal to emit light, whereas those on bothsides thereof are patterns P_(VC) for supplying a reference voltage. Thepatterns P_(VG) are connected to each other on their extensions. Also,the patterns P_(VC) are connected to each other on their extensions.However, it is preferred that the patterns P_(VG) and P_(VC) beseparated from each other.

In the light-receiving device unit 4, the lead pins 43 are arranged soas to hold the circuit board 2 therebetween. Among the lead pins 43,lead pins 43 a and 43 b are secured to patterns P_(a) and P_(b) bysoldering, respectively, and the other lead pins 43 c to 43 e aresecured to their corresponding front or rear face patterns of thecircuit board 2 by soldering, so as to be electrically connectedthereto. The legs 61, 62 of the light-receiving device bracket 6 aresoldered to the patterns P_(VG) on both sides. The body 60 is solderedto the metal enclosure 42 of the light-receiving device unit 4, therebycovering the lead pins 43.

In the light-emitting device unit 5, the lead pins 53 are arranged so asto hold the circuit board 2 therebetween. Among the lead pins 53, leadpin 53 b is secured to the pattern P_(pd) by soldering, and the otherlead pins 53 a, 53 c are secured to their corresponding rear facepatterns of the circuit board 2 by soldering, so as to be electricallyconnected thereto. The legs 71, 72 are soldered to the patterns P_(VC)on both sides. The body 70 is soldered to the metal enclosure 52 of thelight-emitting device unit 5, thereby covering the lead pins 53.

When the wiring patterns are arranged as such, signal lines are heldbetween reference voltage lines, whereby the signal lines can bemaintained at a low inductance, so as to reduce influences of noise uponthe signal lines. Further, since the lead pins are covered with abracket maintained at a reference voltage, their electric shieldingproperty can be enhanced, whereby the intrusion of noise from theoutside and the occurrence of crosstalk between the light-emittingdevice and light-receiving device can be suppressed.

The assembling of this optical transceiver will now be explained. First,the ferrules 41, 51 of the light-receiving device unit 4 andlight-emitting device unit 5 are inserted into their correspondingcylindrical holes 12, 13 formed in the optical connector part 11 of thehousing 1. The brackets 6, 7 are temporarily attached to the deviceunits 4, 5 beforehand by using their protrusions 63, 73.

In this state, using a slit formed in the housing 1, the circuit board 2is inserted therein from the rear side (right side in FIG. 8). When theleading end of the circuit board 2 abuts against a side wall 15 providedwithin the housing 1 as shown in FIG. 11A, the lead pins 43, 53 comeinto contact with the end part of the circuit board 2, so as to hold theend part of the circuit board 2 therebetween, whereby thelight-receiving device unit 4 and the light-emitting device unit 5 areconnected to the circuit board 2. In this state, no soldering iseffected, whereby the lead pins 43, 53 and the legs 61, 62, 71, 72 ofthe brackets 6, 7 are merely in contact with their correspondingpatterns of the circuit board 2. Thereafter, the stopper 3 is insertedinto the circuit board 2 from the rear side thereof, so as to engage thehousing 1, whereby the circuit board 2 is secured to the housing 1.

Subsequently, the bracket holder 8 is inserted such that its protrusions82, 83 are placed between the light-receiving device unit 4 and thelight-emitting device unit 5, and their claws 82 a, 83 a are caused toengage abutments 13, 14 provided in a cutout 17 of the housing 1,whereby the bracket holder 8 is secured to the housing 1. Here, sincethe U-shaped space 85 exists between the protrusions 82, 83, they caneasily fit into the hole between the abutments 13, 14 while inwardlyflexing. After the insertion, the protrusions 82, 83 return to theiroriginal forms by widening due to their elasticity, whereby they canreliably engage the abutments 13, 14 by using the claws 82 a, 83 a.

When the inclined side wall 84 of the holder 8 and an inclined side wall16 of the housing 1 are aligned with each other at the time of insertionas shown in FIG. 11B, the protrusion 81 a of the holder 8 presses theflange part of the light-receiving device unit 4 so as to push itaxially, whereby it can accurately be placed within the hole 12. Thoughnot depicted, a similar relationship holds between the protrusion 82 aand the light-emitting device unit 5. As a result, end face positions ofthe light-receiving device unit 4 and light-emitting device unit 5within the housing 1 in the optical axis direction can accurately bedefined.

If the side wall 84 forms an angle smaller than 40° with the opticalaxis plane (the plane formed by the respective optical axes of thelight-receiving device unit 4 and light-emitting device unit 5,coinciding with the substrate surface of the circuit board 2), it willbe unfavorable since the horizontal movement of the bracket holder 8becomes greater at the time of insertion. If the angle is greater than80°, it will be unfavorable since the pressing effect caused by thesliding becomes insufficient. Therefore, the angle is preferably withinthe range of 40° to 80°.

After the engagement of the bracket holder 8, the lead pins 43, 53appearing from the rear gap of the bracket holder 8 and the legs 61, 62,71, 72 of the brackets 6, 7 are soldered to their corresponding wiringpatterns, while the bodies of brackets 6, 7 are soldered to theenclosures 42, 52 of the light-receiving device 4 and light-emittingdevice 5, respectively. Finally, the attenuator 10 and the case 9 areattached, so as to complete the optical transceiver.

When connecting an optical fiber having an LC connector to the opticalconnector 11, the LC connector engages a claw provided in the opticalconnector 11 of the housing 1, thereby pushing the light-receivingdevice unit 4 or light-emitting device unit 5 toward the board. Thispressure is defined as about 15N=about 1.5 kg. In this embodiment, thepressure is received by the side faces of protrusions 80 a, 81 a, so asto be absorbed within the bracket holder 8 without being transmitted tothe connecting parts of lead pins 43, 53, whereby electriccharacteristics will not deteriorate due to damages in soldered parts.Therefore, stable performances can be maintained even upon repeatedconnecting operations.

Though both of the brackets 6, 7 are placed in this embodiment, theeffect of improving electric characteristics can also be obtained whenone of them is placed alone.

The inventors carried out tests for comparing performances withconventional products in order to verify the foregoing effect of thepresent invention, results of which will now be explained.

FIG. 12 is a graph showing results of EMI (electromagnetic interference)tests on the transmission side carried out for each of ComparativeExample using none of the brackets 6, 7, Example 1 equipped with thelight-receiving device bracket 6 alone, and Example 2 equipped with thelight-emitting device bracket 7 alone. It was seen that the noisesuppressing effect attained by placing a bracket was greater in a higherfrequency region.

FIGS. 13 and 14 are graphs showing results of RES characteristic testson the reception side concerning Example 3 equipped with both of thebrackets 6, 7 and the above-mentioned Examples 1, 2 and ComparativeExample. As shown in the graph, the effect of improving REScharacteristics was seen when placing a bracket on the reception side inparticular.

FIGS. 15A and 15B are charts comparing the transmission waveform (FIG.15A) in Example 3 and the transmission waveform (FIG. 15B) inComparative Example. It was seen that Example 3 yielded a transmissionwaveform more stable than that in Comparative Example due to thedesigning of brackets and wiring patterns, thereby suppressing thecrosstalk amount to 0.38 dB from 0.92 dB of Comparative Example.

FIGS. 16 and 17 are charts showing changes in performances vs. thenumber of attaching/detaching operations in the case where electric andoptical connectors are repeatedly attached/detached in Example 3. As canbe seen from FIGS. 16 and 17, characteristics in Example 3 hardlychanged between before and after 500 attaching/detaching operations,thus exhibiting a sufficient resistance to a number ofattaching/detaching operations.

Without being restricted to optical transceivers of SFP and SFF types,the present invention is favorably applicable to various kinds ofoptical modules having a lead pin structure.

What is claimed is:
 1. An optical module comprising, within a housing, asubstrate having an electronic circuit, and light-emitting andlight-receiving device units each having an optical output or input endconnected to said electronic circuit; wherein a connecting part of saidelectronic circuit to said light-emitting device unit comprisesrespective signal lines for normal and opposite phases arranged on bothsides of a light-emitting device reference voltage line disposed at acenter, and respective reference voltage lines disposed on outer sidesof said signal lines, said signal lines and reference voltage linesbeing electrically connected to respective lead pins extending from saidlight-emitting device unit; and a conductive light-emitting devicebracket which surrounds said lead pins extending from saidlight-emitting device unit and is electrically connected to saidreference voltage lines on both ends of said electronic circuit.
 2. Anoptical module according to claim 1, wherein said light-emitting devicebracket is connected to a metal part of an enclosure of saidlight-emitting device unit.
 3. An optical module comprising, within ahousing, a substrate having an electronic circuit, and light-emittingand light-receiving device units each having an optical output or inputend connected to said electronic circuit; wherein a connecting part ofsaid electronic circuit to said light-receiving device unit comprisesrespective reference voltage lines arranged on both sides of a signalline, said signal line and reference voltage lines being electricallyconnected to respective lead pins extending from said light-receivingdevice unit; and a conductive light-receiving device bracket whichsurrounds said lead pins extending from said light-receiving device unitand is electrically connected to said reference voltage lines on bothends of said electronic circuit.
 4. An optical module according to claim3, wherein said light-receiving device bracket is connected to a metalpart of an enclosure of said light-receiving device unit.